Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!umd5!purdue!i.cc.purdue.edu!j.cc.purdue.edu!pur-ee!uiucdcs!uxc.cso.uiuc.edu!uxe.cso.uiuc.edu!mcdonald
From: mcdonald@uxe.cso.uiuc.edu
Newsgroups: comp.lang.c
Subject: Re: volatile isn't necessary, but it's
Message-ID: <225800020@uxe.cso.uiuc.edu>
Date: 16 Apr 88 15:10:00 GMT
References: <7794@alice.UUCP>
Lines: 32
Nf-ID: #R:alice.UUCP:7794:uxe.cso.uiuc.edu:225800020:000:1770
Nf-From: uxe.cso.uiuc.edu!mcdonald    Apr 16 09:10:00 1988


>>In article <7794@alice.UUCP> dmr@alice.UUCP writes:
>>Has anyone else noticed that a lot of the more peculiar things that X3J11
>>has added (volatile, and especially noalias) are there for the
>>benefit of compiler writers and benchmarkers, and not for the user?
...........

>It seems the compilers are now doing things like unrolling loops with
>constant bounds, and generating in-line code for what are supposed to
>be library routines, like strcpy and memcpy.  This makes for much
>faster benchmarks, but makes large (source) programs generate such
>large object files that they no longer fit in the target systems'
>memory space.


I think it HIGHLY desirable that compiler vendors provide the tools to get
the fastest running programs! I and my students get tired of waiting
30 minutes to hours for some program to run! The MS-DOS compiler business
has gotten so competitive that the users are being well served indeed!
In the Microsoft case, you've got /Ox (breaks quite a bit of code because
they haven't implemented "noalias" :-)  ) which is equivalent to
    /Oailt /Gs, which implements, in order, optimizations unsafe in 
the presence of aliases, inline expansion of certain things, loop
optimizations, and general optimization for fastest time, plus
the /Gs to remove run-time stack checking. On the other hand, they
have /Os, which optimizes for smallest size (but only makes a small
difference).  The BIGGEST gain in speed in some cases also reduces size:
/Gc, which changes to globally using a more efficient calling convention,
but also requires declaring certain thing with the "cdecl" keyword,
which in turm starts another religious war in "comp.lang.c" :-) :-)
     I think that these people should be congratulated, not pilloried!

Doug McDonald